The Obama administration entered the fierce national debate over voting rights, rejecting South Carolina’s new law requiring photo identification at the polls and saying it discriminated against minority voters.

Friday’s decision by the Justice Department could heighten political tensions over eight state voter ID statutes passed this year, which critics say could hurt turnout among minorities and others who helped elect President Obama in 2008. Conservatives and other supporters say the tighter laws are needed to combat voter fraud.

Justice Department lawyers, facing intense pressure from civil rights groups to act against the new laws, are still reviewing Texas’s statute.

In its first decision on the laws, Justice’s Civil Rights Division said South Carolina’s statute is discriminatory because its registered minority voters are nearly 20 percent more likely than whites to lack a state-issued photo ID. Under the 1965 Voting Rights Act, South Carolina is one of a number of states that are required to receive federal “pre-clearance” on voting changes to ensure that they don’t hurt minorities’ political power.

“The absolute number of minority citizens whose exercise of the franchise could be adversely affected by the proposed requirements runs into the tens of thousands,” Assistant Attorney General Thomas E. Perez said in a letter to South Carolina officials.

South Carolina Gov. Nikki Haley (R) called the decision “outrageous” and said she plans to seek “every possible option to get this terrible, clearly political decision overturned so we can protect the integrity of our electoral process and our 10th Amendment rights.”

The law, passed in May and signed by Haley, requires voters to show one of five forms of photo identification. The state can now try to get the law approved by a federal court or seek reconsideration from Justice.

South Carolina cited the need to fight voter fraud in defending the measure. Whether election fraud exists to any significant degree and how extensive it may be is the subject of a divisive national debate. Some conservatives have long argued that fraud is a serious problem, but Perez said that South Carolina’s submission “did not include any evidence or instance” of fraud not already addressed by state laws.

The federal action — the first time the government has rejected a voter-identification law in nearly 20 years — signals an escalating national legal battle over the laws as the presidential campaign intensifies. The American Civil Liberties Union and another group recently filed a federal lawsuit contending that Wisconsin’s new voter-identification measure is unconstitutional.

Laws approved in Mississippi and Alabama also require federal approval but have not yet been submitted to the federal government. States can get such approval for changes to voting laws from Justice, a federal court in the District or both.

It is unclear if the four states not subject to the Voting Rights Act requirement — Wisconsin, Kansas, Rhode Island and Tennessee — will face challenges to their laws. Justice lawyers could file suit under a different provision of the act, but the department has not revealed its intentions.

The voter-identification measures, enacted mostly by Republican legislatures, also impose restrictions on early voting and make it harder for former felons to vote. The Justice Department is also reviewing electoral changes in Florida that reduce the number of days for early voting.

But it is the voter-identification laws that have aroused the most fury on the left, with some comparing them to the poll taxes once used to keep minorities from voting in the segregated South. Opponents of the new laws say they would discriminate against minorities, and others such as low-income voters, because some don’t have the necessary photo ID and lack the means to easily obtain ID cards.

One study estimated that the changes could keep more than 5 million voters from the polls. But the laws have proven popular, according to some surveys. Last month, Mississippi voters easily approved an initiative requiring a government-issued photo ID at the polls.

The ACLU and other civil rights groups praised the Justice Department’s decision on South Carolina’s law, with NAACP President Benjamin Jealous saying it “ensures all eligible South Carolinians will have access to the ballot box in 2012 and beyond.”

Jon Greenbaum, chief counsel for the Lawyers’ Committee for Civil Rights Under Law, said the Justice Department “applied the law faithfully here and really did an excellent job analyzing if the [South Carolina] law would have a discriminatory effect.”

Supporters of the law were equally expansive in their criticism. Hans von Spakovsky, a senior legal fellow at the conservative Heritage Foundation, said the decision “was purely political and driven by ideology.”

Noting that courts have found laws requiring voter identification in Georgia and Indiana to be nondiscriminatory, “they are going against their own precedents and other court decisions,” von Spakovsky added.

In South Carolina, Republican Party Chairman Chad Connelly called requiring voter identification “a common-sense safeguard. . . . The Obama administration has once again decided that Washington knows best.’’

The Justice Department’s decision came after Attorney General Eric H. Holder Jr. signaled a tough stance on the new state laws in a Dec. 13 speech. He expressed concern about the measures, saying, “Are we willing to allow this era — our era — to be remembered as the age when our nation’s proud tradition of expanding the franchise ended?”

At the same time, Holder vowed not to let politics affect his department’s review of the laws. “We’re doing this in a very fair, apolitical way,” he said in a recent interview with The Washington Post. “We don’t want anybody to think that there is a partisan component to anything we are doing.”

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